Cotton stretch yarns by graft polymerization with vinyl monomers followed by back-twisting or falsetwisting



United States Patent ()fifice 3,377,163 Patented Apr. 9, 1968 3,377,163 QOTTON STRETCH YARNS BY GRAFT POLYM- ERIZATEON WITH VINYL MONOMERS FOL- LOWE!) BY BACK-TWISTING R FALSE- TWISTENG Carl Hamnlainen, Metairie, Hubert H. St. Marcl, New

Orleans, and Albert S. Cooper, Jr., Metairie, La., assignors to the United States of America as represented by the Secretary of Agriculture No Drawing. Filed July 13, 1966, Ser. No. 564,759 6 Claims. (Cl. 57164) A non-exclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to the production of stretch textile materials by grafting acrylonitrile and other vinyl monomers to cellulosic yarns of normal and high-twist construction followed by false-twisting or back-twisting to produce stretch yarns and then weaving the resultant yarns into fabric to produce fabrics with stretch properties.

The terms back-twisting and in the specifications and claims of this invention with specific meaning. In back-twisting, plied yarns which have been grafted with select compounds are then untwisted past their neutral ply twist. Then these are allowed to relax, and as they tend to return to the highly twisted state they tend to form multiple helical coils. It is these helical coils which give the yarn its stretch.

False-twisting, on the other hand, is based on the principle that if a stationary yarn is twisted at its center an equal amount of opposite twist will be imparted to each half, and the algebraic sum of the added twist throughout the length of the yarn will be zero. In the false-twisting machine the spindle rotates continuously as the yarn moves forward so equilibrium may be reached; plied yarns twisted in one direction enter the spindle, where it is twisted in the opposite direction, then heatset; and as it leaves the spindle it is restored to its original twist.

Most stretch cotton fabrics are going into apparelslacks, blouses, pajamas, uniforms for waitresses and nurses, and other such garments, but upholstery and slipcover fabrics are being made. Stretch adds comfort and allows the fabrics to give at knees and elbows without unsightly bagging.

Stretch yarns have been produced by treating highlytwisted yarns with crosslinking agents (Brown, J. J., and Ruppenicker, G. F., Jr., Textile Industries 126 (8) 102 (1962)), heat-curing them in this highly-twisted state, and then back-twisting beyond the neutral ply twist. Stretch has also been obtained by shrinking the yarns about to 70% by tensionless mercerization (Sloan, W. G., Murphy, A. L., Hoffman, M. J., Moore, H. B., and Cooper, A. S., In, Textile Research 1., 33, 191 (1963)) followed by subsequent washing and drying without restretching the yarn. Highly chemically modified yarns such as acetylated yarns, have been heat-set followed by twisting techniques to produce stretch. This results from the deformation of the yarns which are thermoplastic and maintaining the deformed structure after twisting. Although thermoplastic-like properties can also be imparted to cotton by graft polymerization, the thermoplasticity is of somewhat different nature than that obtained by simple chemical substitution. Stretch can be imparted without heatsetting since grafting tends to fix or set the yarn. Thus, highly-twisted yarns can be treated with a graft polymerizing agent and then back-twisted to obtain stretch properties.

false-twistin are used 8 Mercerization causes a great deal of swelling in cellulosic fibers with disruption of hydrogen bonds. These bonds are re-established in new positions after washing and drying procedures. Disrupting the geometry of these highly-swollen yarns as by back-twisting results in a coiled or crimped structure with stretch properties.

For the purpose of this invention the cellulosic materials include cotton, viscose, cuprammonium rayon, partial esters of cellulose such as cellulose acetate, cellulose propionate, cellulose nitrate, and the like; partial ethers of cellulose such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, cyanoethylated cellulose, and the like; and also other natural cellulosic fibers, such as jute, hemp, linen, ramie, sisal, and the like, may be used; also wood, wood products, pulp, and paper may be included. Mixtures or blends of fibers are intended to be included.

Although polymerization of olefinic monomers within the fibers of cellulosic materials and grafting of polymers to the cellulose molecules becoming an integral part of the material has been disclosed, no mention has been made of the use of this product for possible application to stretch.

The graft polymerization process may be carried out at temperatures between about from 20 to 200 F., but preferably at temperatures between about from 50 to 120 F. The grafting process may be carried out under pressure or partial vacuum, but it is preferred to utilize atmospheric pressure inasmuch as the reaction runs favorably at this pressure. Covering the reaction with a blanket of nitrogen gas or carbon dioxide to eliminate the atmospheric oxygen would enhance the reaction but it is not absolutely essential. We have found that we get appreciable reaction when the cellulosic material is completely submerged in the reaction solution.

The grafting process may be carried out at any pH value up to 3.5. The pH value is usually between land 2 in aqueous polymerization reaction for optimum reac: tion. a

In practice the grafting process is generally carried out in aqueous solution when the monomer has appreciable water solubility, and in aqueous emulsion when the monomer is only partially soluble or is essentially insoluble in water. It can also be carried out by a vapor phase technique in which the cellulosic material is permeated by the hot vapor of the monomer.

Among the monomeric polymerizable compounds which may be used in practicing this invention are those containing polymerizable H C=C groups. This includes vinylidine and/ or vinyl compounds. More specifically the following polymerizable monomers may be used: styrene and substituted sytrenes, polymerizable acrylic compounds, such as acrylic acid and its homologs, such as methacrylic acid and their esters of monohydric alcohols, such as methyl, ethyl, propyl, and the like; and the acrylic type acid esters of polyhydric alcohols, such as ethylene glycol and the like. Still further, as the polymerizable monomer, one may use allyl compounds, such as allyl alcohol or substituted allyl esters, such as allyl acetate, allyl acrylate, allyl cyanurate, and the like. Still further, one may make use of the vinyl or vinylidine esters, such as vinyl acetate, vinyl chloride, vinylidine chloride, and the like. Othervinyl compounds, such, as vinyl ethyl ether, vinyl pyridine, and the like may also be used. Additionally, one may make use -of the unsaturated polymerizable amides such as acrylamide, methacrylamide, methylene bisacrylamide, and the like, or the nitriles, such as acrylo nitrile, methacrylonitrile and the like. Whenever desirable, these polymerizable monomers may be used either singly or in combination with one another.

Any method capable of initiating free radicals on the polymeric alcohol chain, i.e., cellulosic backbone, can be used in the practice of the present invention. These may 3 include persulfate, ferrous ion-peroxide, ceric ion, highenergy radiation, and others.

In the practice of our invention we have used the ceric ion activation procedure. The amount of ceric compound Which is utilized may be varied over fairly Wide limits. For example, one may utilize from about to 10 mole of ceric ion per liter of reacting solution. Preferably we would use .002 mole to 0.012 mole ceric ion per liter and nitric acid of .02 to 0.12 molarity. Ceric ion is preferably introduced into the reaction mixture in the form of a ceric salt. Among the salts recommended for use are ceric nitrite, ceric sulfate, ceric ammonium nitrate, ceric ammonium sulfate, and the like. These compounds may be employed singly or in combination with one another. Also ceric compounds which are capable of forming ceric salts in situ under the acid condition of the polymerization reaction such as ceric oxide and the like may be used.

In general, the time required to achieve a desired degree of graft polymerization may be determined empirically. Thus, the amount of polymer weight add-on in the cellulosic material is an indication of the extent of the reaction. Where the amount of ceric ion and monomer is known, suitable reaction times may be readily established to achieve the desired degree of polymerization.

Definition:

Twist multiplier (Tlll) or t.p.i. TMX yarn number The yarn constructions used in the practice of this invention to obtain stretch properties were 14/2 high-twist cotton yarn with 4.0 TM in the Z-direction in the singles and 7.0 TM in the Z-direction in the ply; 24/2 normaltwist cotton yarn with 4.0 TM in the Z-direction in the singles and 4.0 TM in the S-direction in the ply; 24/2 hightwist cotton yarn with 4.0 TM in the Z-direction and 7.0 TM in the Z-direction in the ply; and 35/2 high-twist cotton yarn with 4.25 TM in the Z-direction in the singles and 7.0 TM in the Z-direction in the ply. This does not preclude that other constructions could not be used.

It was preferable to scour the yarn prior to the grafting treatment for best add-on of graft polymer.

After the grafting treatment the normal-twist yarns were false-twisted to 44 t.p.i. at the rate of 20 yards per minute at 200400 F. to obtain stretch properties. The grafted high-twist yarns were back-twisted TM in the S-direction with 51.5 machine t.p.i. Heating the grafted yarns two minutes at 360 F. prior to back-twisting improved the stretch properties somewhat, but is not essential to the invention.

In describing our invention briefly to a person skilled in the art we would say that this invention consists of two distinct and separate processes for imparting improved stretch properties to cellulosic textiles, the one comprismg:

and the other comprising:

(a) grafting onto cellulosic yarns of high-twist construction a vinyl monomer from an aqueous 2% to 6% solution containing the said vinyl monomer selected from the group consisting of acrylonitrile and methyl 'acrylate and as a catalyst ceric ammonium nitrate and nitric acid,

(b) washing and equilibrating the treated yarns in an ordinary manner,

(c) back-twisting the grafted high-twist yarns, and

(d) allowing the back-twisted yarns to relax in water containing a wetting agent.

In order that the concept of the invention may be more fully understood, the following examples are set forth, primarily for the purpose of illustration and any specific enumeration of detail contained therein should not be interpreted as a limitation of the case except as indicated in the appended claims.

EXAMPLE 1 A skein of 12/3 scoured cotton yarn weighing 4.57 grams was treated in an open beaker with 250 ml. 6% aqueous acrylonitrile solution containing 30 ml. ceric solution (0.1M Ce(NH (NO 1M HNO for a period of 30 minutes at room temperature (78 F.). After washing the treated skein and drying it to air equilibrium in moisture, it weighed 6.48 grams, a weight increase of 41.8%. The sample was extracted with hot dimethylformamide (DMF) for five hours and again washed and air equilibrated. Its extracted weight was 6.11 grams corresponding to a residual polymer weight add-0n of 33.5%. This shows that the polymer is firmly attached to the cellulose.

EXAMPLE 2 A skein of 35/2 high-twist plied cotton yarn scoured and dyed brown weighing 9.43 grams was treated in an open beaker for 30 minutes at room temperature (77 F.) in a solution containing 400 ml. 6% aqueous acrylonitrile and 30 ml. ceric solution (0.1M Ce(N'I-I (NO 1.0 M HNO After washing and air equilibrating the sample weighed 10.68 grams representing a weight add-on of 13.3%. The sample was heated in a forced draft oven for two minutes at 360 F., after which it was then backtwisted. After back-twisting the yarn was made into a skein, soaked in hot tap water to relax and allowed to dry flat on a towel, The skein shrunk to /3 of its original length upon drying. The shrunken skein of 8 inch length was stretched with a 200 gram weight to 16 inch length, and left for 24 hours when it had stretched to 19 /2 inches. On removing the weight the sample shrank immediately to 15 inches. Two hours later it was 13 /2 inches, and at the end of 24 hours to 10 /2 inches. It had excellent resiliency and springiness.

EXAMPLE 3 Sample No. Time of Reaction, Weight Add-on,

Minutes Percent EXAMPLE 4 Duplicate skeins of 14/2 scoured high-twist yarn each weighing between 6 and 7 grams were reacted for 15, 30, and 60 minutes in an open beaker at room temperature (80 F.) in a solution of 6% aqueous acrylonitrile containing 0.002 molar concentration of ceric salt (ceric amomnium nitrate) and 0.02 molar concentration of nitric acid. After washing and air equilibrating the samples were weighed. They showed a progressive increase in weight (polymer add-on) with an increase in time of reaction as seenin the following table:

Sample No. Time of Reaction, Weight Add-on,

Minutes Percent The weight add-on was at a lower level than in Example 3 in which a higher ceric concentration was used.

EXAMPLE 5 STRETCH YARN PROPERTIES (Serigraph, Threads) 1 v Sample Number Tex Breaking Elongation Stretch 5th N 0. Strength at Break Cycle (Per- (1bs.) (Percent) cent) Untreate 1 85 92 12 2. 0 176-1 100 78 29 176-2.- 94 79 41 25 175-1 2 96 67 47 175- 96 77 62 43 175-3 100 66 71 79 175-4- 91 68 56 171-1 91 68 58 41 171-2 93 69 43 27 70-1 101 61 111 l702. 101 63 74 58 170-3 2 105 56 132 -4-..- 111 57 145 119 1 Multiple strand test specimens were made by winding 40 strands of yarn on a seriplane board, ref. .1. J. Brown and Geo. F. Ruppernicker, Jr., Textured Cotton Yarns, Textile Industries, 126 (8): 102 (1962).

2 Heated 2 minutes at 360 F.

There is an increase in yarn size with an increase in polymer add-on. There is also some loss in strength. However, there is a large increase in elongation at break and stretch in the 5th cycle with the increase in polymer content. Heating the sample increased these stretch properties somewhat.

EXAMPLE 6 Sample No. Time of Reaction, Weight Add-on,

Minutes Percent The washed air equilibrated samples show a progressive increase in polymer add-0n with an increase in time of reaction but not to the extent as with the 6% acrylonitrile solution in Example 4.

, EXAMPLE 7 Skeins of 24/2 scoured,high-twist yarn weighing approximately 5 grams each were reacted in an open beaker with 4% aqueous methylacrylate solution containing 0.002 molar concentration of ceric salt (ceric ammonium nitrate) and 0.02 molar concentration of nitric acid at room temperature (72 F.) for varying periods of time according to the following table:

Sample N 0. Time of Reaction, Weight Add-on,

Iinutes Perre .t

The washed air equilibrated samples show a rogressive increase in polymer add-on with an increase in time of reaction.

EXAMPLE 8 Selected samples from Examples 6 and 7 were variously heated and then back-twisted. The physical properties of these stretch yarns are shown in the following table:

PHYSICAL PROPERTIES (Serigraph, 40 Threads] Sample Tex Brk. Elong. Stretch N 0. Heat Tretment N o. Strg. At Brk. 5th Cycle (Lbs) (Percent) (Percent) At the low level of grafted acrylonitrile add-on (10- l2%) heating prior to back-twisting had very little efiect on the stretch properties. The samples grafted with methyl acrylate showed considerably less stretch than the acrylonitrile grafted samples even at the high polymer add-on of 45% (Sample 188-4).

EXAMPLE 9 Eight 500 yarn skeins of 24/2 normal-twist yarn and eight 500 yard skeins of 24/2 high-twist yarn were treated 40 minutes at room temperature with 6% aqueous acrylonitrile solution containing 0.002 molar concentration of ceric salt (ceric ammonium nitrate) and 0.2 molar concentration of nitric acid. After washing and air equilibrating the normal-twist yarns had a weight increase of 30 to 36% and the high-twist yarns had a weight increase of 14 to 21%. The treated normal-twist yarns were falsetwisted at 265 F. and the treated high-twist yarns were back-twisted with no heat treatmen. These yarns were woven into fabric using them as filling yarns with 40 picks per inch. The stretch properties of the fabric in fillingwise direction are shown in the following table:

STRETCH PROPERTIES OF FABRIC 1 load at 10 inch gauge length. The recovery measurements were made after one minute and 24 hours of relaxation.

The fabric from the acrylonitrile grafted normal-twist yarns had the best overall stretch properties in that it had the lowest growth after 24 hours recovery from five cyclic loadings. The fabric from the acrylonitrile grafted hightwist yarn was stronger but its elongation was slightly less and it had a greater amount of growth.

We claim: 1

1. A process for imparting improved stretch properties to cellulose textiles comprising:

(a) grafting onto cellulosic yarns of normal-twist construction a vinyl monomer from an aqueous 2% to 6% solution containing the said vinyl monomer selected from the group consisting of acrylonitrile and methyl acrylate and as a catalyst ceric ammonium nitrate and nitric acid,

(b) washing and equiiibrating the treated yarns,

(c) false-twisting the grafted normal-twist yarns, and

((1) allowing the false-twisted yarns to relax in water containing a wetting agent.

2. The process of claim 1 wherein the vinyl monomer is acrylonitrile. g

3. The process of claim 1 wherein the vinyl monomer is methyl acrylate.

4. A process for imparting improved stretch properties to cellulosic textiles comprising:

(a) grafting onto cellulosic yarns of high-twist construction a vinyl monomer from an aqueous 2% to 6% solution containing the said vinyl monomer selected from the group consisting of acrylonitrile and methyl acrylate a catalyst ceric ammonium nitrate and nitric acid,

(b) washing and equilibrating the treated yarns,

(c) back-twisting the grafted high-twist yarns, and

10 (d) allowing the back-twisted yarns to relax in'water containing a wetting agent. 5. The process of claim 4 wherein the vinyl monomer is acrylontirile. r' 6. The process of claim 4 wherein the vinyl monomer is methyl acrylate.

References Cited UNITED STATES PATENTS 2 2,463,618 3/1949 Heberlein et a1. 57l57 3,127,732 4/1964 Brown et al. 57-164 3,285,690 11/1966 Cooper et al. 8116.3

JOHN PETRAKES, Primary Examiner. 

1. A PROCESS FOR IMPARTING IMPROVED STRETCH PROPERTIES TO CELLULOSE TEXTILES COMPRISING: (A) GRAFTING ONTO CELLULOSIC YARNS OF NORMAL-TWIST CONSTRUCTION A VINYL MONOMER FROM AN AQUEOUS 2% TO 6% SOLUTION CONTAINING THE SAID VINUL MONOMER SELECTED FROM THE GROUP CONSISTING OF ACRYLONITRILE AND METHYL ACRYLATE AND AS A CATALYST CERIC AMMONIUM NITRATE AND NITRIC ACID, (B) WASHING AND EQUILIBRATING THE TREATED YARNS, (C) FALSE-TWISTING THE GRAFTED NORMAL-TWIST YARNS, AND (D) ALLOWING THE FALSE-TWISTED YARN TO RELAX IN WATER CONTAINING A WETTING AGENT. 